I feel like the heroric epic is being a bit underrated here. The ability to build it comes pretty early; iron working is one of those that most people go for at a reasonably early time, although this may have changed with iron being discoverable earlier. Anyway, by the time you CAN build it, you shouldn't have more than 3ish cities anyway unless you are an utter expansionist whore, so you only need to build a couple of barracks to unlock it for your unit producing city located conveniently next to your iron deposit. And now with caravans you can route production about as necessary to speed up the process so your queue isn't totally dragged down by the extra barrackses (say that outloud and not use a gollum hobbitses voice I dare you) that you won't even use later. The bonus to attack isn't totally amazing but is a nice addition with the upgrades from all of the XP buildings later.
Is it THE BEST. BUILDING. EVER? No, it can be skipped. Is it worthless? I don't think so, I -always- build it! Being able to pinch purchase units that have a smidgeon extra power when you're at a numerical or even technological disadvantage can help tremendously.